A randomized trial indicating that surgical masks are not inferior to N95 masks in protecting healthcare workers against COVID-19 has sparked international criticism.
The study's senior author is John Conly, MD, an infectious disease specialist and professor at the Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada, and Alberta Health Services. The findings are not consistent with those of many other studies on this topic.
Commenting about Conly's study on Twitter, Eric Topol, MD, editor-in-chief of Medscape, wrote, "It's woefully underpowered but ruled out a doubling of hazard for use of medical masks."
The study, which was partially funded by the World Health Organization (WHO), was published online November 29 in Annals of Internal Medicine.
This is not the first time that Conly, who also advises the WHO, has been the subject of controversy. He previously denied that COVID-19 is airborne — a position that is contradicted by strong evidence. Last year, Conly made headlines with his controversial claim that N95 respirators can cause harms, including oxygen depletion and carbon dioxide retention.
A detailed examination by the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, Minneapolis, pointed out numerous scientific flaws in the study, including inconsistent use of both types of masks. The study also examined healthcare workers in four very different countries (Canada, Israel, Egypt, and Pakistan) during different periods of the pandemic, which may have affected the results. Furthermore, the study did not account for vaccination status and lacked a control group. CIDRAP receives funding from 3M, which makes N95 respirators.
In a commentary published alongside the study, Roger Chou, MD, professor of medicine at Oregon Health & Science University in Portland, said that the results were "not definitive," with "a generous noninferiority threshold" that is actually "consistent with up to a relative 70% increased risk … which may be unacceptable to many health workers."
Lead study author Mark Loeb, MD, professor of infectious diseases at McMaster University in Hamilton, Ontario, Canada, defended the findings. "The confidence intervals around this, that is, what the possible results could be if the trial was repeated many times, range from −2.5% to 4.9%," he told Medscape. "This means that the risk of a COVID-19 infection in those using the medical masks could have ranged from anywhere from 2.5% reduction in risk to a 4.9% increase in risk. Readers and policy makers can decide for themselves about this."
"There is no point continuing to run underpowered, poorly designed studies that are designed to confirm existing biases," Raina MacIntyre, PhD, professor of global biosecurity and head of the Biosecurity Program at the Kirby Institute, in Sydney, Australia, told Medscape. "The new study in Annals of Internal Medicine is entirely consistent with our finding that to prevent infection, you need an N95, and it needs to be worn throughout the whole shift. A surgical mask and intermittent use of N95 are equally ineffective. This should not surprise anyone, given a surgical mask is not designed as respiratory protection but is designed to prevent splash or spray of liquid on the face. Only a respirator is designed as respiratory protection through both the seal around the face and the filter of the face piece to prevent inhalation of virus laden aerosols, but you need to wear it continually in a high-risk environment like a hospital."
